Going Backpack Mobile!

[hertzian]

The 12120 would be ok. I use a small range of these depending on the setup. If given a choice, look for the larger terminals, ie the F2 terminals.

A quick approximation - assuming the battery is fully charged, and if your 8900 uses 1amp on receive, you could run it for about 6 hours before you reached the 50% DOD mark. You may be able to run it for maybe 7-8 hours with a much deeper discharge (providing the voltage isn't too low for the 8900 at that point) if you aren't concerned about getting 1000 cycles out of it. Obviously transmitting for long periods at high power will cut your time down.

A quickie way to tell if you are at the 50% mark, is to measure the open circuit voltage after a few hours (no charge, no load) which would be about 12.22 volts. Note that you may not see full capacity until you have cycled it about 10-20 times, so actually using it is a good thing.

How long would it take to recover from 50% DOD? Assuming we are taking advantage of an agm's ability to use up to .25C on average, powersonic provided a nice formula that works pretty well in the real world provided your day is perfectly bright:

6a / 3a * 1.76 = 3.52 hours (missing capacity / charge current * offset needed to achieve full charge) Example: Here the charge current was maxed out with a 60 watt panel at about C/4 (12 / 4 = 3 a. 6a missing / 3a charge * 1.76 = 3.52 hours) 4 hours is considered the average "solar insolation" hours (different from normal daylight hours), so it would take one average solar day to recharge it fully. Maps are available to determine your location's solar insolation hours.

Try to avoid any that are older than 6 months - maybe a year tops. Also 12.5 - 12.6v out of the box is my personal minimum before I consider a refund or replacement for something newer or that has been maintained properly before purchase.

Morningstar is a major player in the solar charge controller marketplace. Another good one to consider is Steca or Samlex for these small setups.

[RESlusher]

Thanks for the info Master Yoda! I am grateful.

I was thinking that the 12120 was an OK balance of charge and weight. If I'm using it out in the in a real world, SHTF type situation I figure I'd only be transmitting for a couple minutes at the top and/or bottom of the hour or whatever plan has been worked out ahead of time in the area where I'm headed Any other time I'd just be listening. I probably wouldn't be leaving it powered on all the time.

Thanks again for the info! I do appreciate it.

73!

[hertzian]

Happy to help. Note that the "pwm" or pulse-width-modulated style of charging models is appropriate here. The other common style "mppt" or maximum power point tracking, is not really worth the investment at these low power levels, despite the hype unless you know you really need it.

One consideration about mppt is that it is a dc-dc switching circuit, and may have noise issues - one reason I stick to pwm. Mppt is also good for when you have very long runs of DC cabling, and want to run high-voltage setups, like 24 to 48 volts panels which then gets converted back to 12v, so you can run much thinner gauge wiring. In some cases, people buy "GTI" (grid-tie) panels which are higher voltage designed for off-grid use and use an mppt to convert down. For you, the nominal 12v panel (about 17-22 volts open circuit) is fine.

In any event, try to keep your cabling as short as necessary. In your situation, it shouldn't be a problem right around the camp / hike site, but consult wiring charts for safety and voltage drop considerations if you run very long lines. Typically one tries to go no lower than maybe 3 percent voltage drop. Keep the controller near the battery rather than close to the panel.

[RESlusher]

Is this PWM / MPPT marked on the packaging somewhere or is it just something I'll need to know?

What about a regular battery charger like one would keep in the garage? Any preferences?

[hertzian]

You should be able to see it in the description. For example, Morningstar sells both pwm and mppt types. Mppt is considerably more costly. The small Sunguard 4.5a is pwm only. The other models such as Sunsaver, Tristar, etc come in both flavors. Steca's prominently describe pwm as well. In your application, pwm is just fine.

NOTE: many controllers assume that all sealed lead acid VRLA types like ours are gel! You do NOT want to use gel settings. The key is to avoid the brain-dead labeling, and look for the actual voltage setting. For example, if they offer a switchable "sealed" value of 14.1 volts, and a "flooded" value of 14.4v, choose flooded even though you are AGM. Go by voltages. Some of the dumb labeling is just being over-protective for the consumer that doesn't even know what the chemistry of the battery is, so they take the most protective way out. If you know your chemistry, and you do, choose the proper voltage for agm, which is typically 14.4 - 14.7 volts.

Chargers! Do NOT use the typical dumb automotive charger. There is a lot of hype out there, but all we're looking for is a nice intelligent 3-stage charger - bulk / absorb / float.

There are many out there - usually heavy on marketing and hip videos. I formerly used to use Deltran Battery Minders, but lately have switched to NOCO Genius since they allow for some user choices like switching between a normal and true agm setting. I use the agm setting, but you aren't forced to. I like being given a choice. The NOCO's are switching types, so they are light but yes, can be noisy on HF, so I don't leave them floating all the time. I just use them to get back up to a full charge when I don't have the solar time to do so with the panels and disconnect them when I store the battery for next outing. Check on the battery every 90 days or so, and give it a boost and disconnect again for the next interval. Or just put the solar setup in the backyard for a few hours.

I think the Noco Genius G1100 would be a very nice fit for your setup. Since an agm can basically stand C/4 inrush current, that 12ah battery could easily take 3amps inrush. Here, the 1.1amp rating of the 1100 is fine since you have the time on AC power. You could go with something smaller, but I've found in practice that going much below C/15 for agm's are in the "tickling" category and agm's don't like to be tickled. In other words, work that thing. Properly taken care of, your agm battery will most likely die of old age long before you run out the cycles.

Note that if you properly care for your battery, you won't be hoodwinked by all the anti-sulphating / zombie battery revival gadgets. Good maintenance is preferable to abuse.

[RESlusher]

NOCO Genius G1100...got it! Thanks for another tip!

My plan is to have two batteries. One is with the radio in a Faraday cage made from an ammo can and the second on the charger (assuming it's been used).

[hertzian]

Well, think the NOCO over since it is a dc-switching (rf-noisy) circuit. It is however pretty light and compact. I have the G3500 model, and it can be heard on HF up to 6 meters, but 2m through 70cm seems clean.

If you don't mind a little additional bulk and weight, a much rf-quieter linear-type charger like the Battery Tender PLUS 12V @ 1.25a would be a bit more ideal if you are charging and operating very close to each other.

[RESlusher]

Thanks! I'll definitely think about it.

My plan though is that I can use the battery charger when I'm home and not transmitting to keep the battery(s) topped off. If I'm out in the bush for any length of time I'll use the solar panel setup.

Again, I can't thank everyone here enough for all the advice and guidance you've given on this. As soon as I can get a few things off the Honey-Do I'm going to get started on this little project.

[John599nj]

You got some great advice here but as far as radio choice if I had to do it again instead of buying 5 radios just buy something like the Yaesu 857d or Icom 706 mk2g. It's small it's all band you can use it base, mobile or potable and you can go low power up to 100 watts. Just my 2 cents

[prcguy]

The Icom 706 series is not a good choice for battery operated portable use due to high rx current around 1.8A. The Yaesu FT-857 is better suited. I have both and love the 706MKII for the vehicle but never for backpack use!
prcguy

Originally Posted by John599nj

You got some great advice here but as far as radio choice if I had to do it again instead of buying 5 radios just buy something like the Yaesu 857d or Icom 706 mk2g. It's small it's all band you can use it base, mobile or potable and you can go low power up to 100 watts. Just my 2 cents

[RESlusher]

Well, I finally got started on the backpack portable Yeasu FT-8900.

To reduce the weight (and cost) I went with 1/2" PVC rather than copper tubing. I was concerned at first about the overall strength of the PVC; but when I got it all put together it was really quite strong.

Here's a pic of the frame dry fitted. Once I get the sheet metal bent to fit inside it then I'll glue everything together.



Before I do the final assembly I'll try to make a YouTube video. I didn't do it now because I figure you guys all know how to operate a tape measure and tubing cutter.

[Sportster77]

Originally Posted by gewecke

Optima Part No. D31M - BlueTop Deep Cycle Marine Batteries

73,
n9zas

Odessy and XS also make AGM batteries and are available in smaller sizes than Optima.

http://www.summitracing.com/search/D...?Ns=Rank%7cAsc

[hertzian]

RESlusher - nice job! Keep us posted on that homebrew pack!

Some battery notes - be aware that there are TWO types of Optima blue-tops - one designed strictly for starting (blue/black) and the other that is dual-purpose hybrid (blue/white). You'd want the latter although I see no reason not to get a yellowtop unless you really want the extra posts.

Don't over-torque the side posts if they have them. Use dual-wrenches, etc so you don't damage them, and never use the side posts for things like winches, etc.

However I doubt that RESlusher would be humping these around.

I use some Odyssey PC-535 (13ah) and PC625 (18ah, cheaper than the 535) motorcycle-type dual-purpose batteries currently for my solar stuff powering radios. Thing is, you can hit these hard with a lot of current to cut down on recharge time, BUT, the cost of admission is high - 0.4C miminum if you are at 80% DOD, and maybe 0.3C if you are only half way discharged at 50% DOD. Anything less will be frustrating. That's a LOT of panel to take with you as well.

Something smaller to consider are the Hawker-Cyclon batteries, basically baby-Odyssey's in an approximate D-sized shape. I'm currently running two 6V, 5ah monoblocks in series for a 12V battery for other stuff. Watching people's expressions when they see an 85 watt panel (4.5a) hooked up to a 5ah SLA (via charge controller of course!) is fun. The Cyclons can take it although I personally don't take these further than 1C current on a Constant-Voltage CV type controller.

Also note that Sears Diehard Platinums are really Odyssey's, but then again, not available in small backpack sizes.

I'm not exactly sure that going totally solar with the Odysseys won't invalidate the warantee with it's pretty strict IUU-profile charging specs. Optima's charging specs are very easy to comprehend, but here too not sure about warantee.

[RESlusher]

Nah, that'll be a little much for me. I'm packing one Werker 12V 12ah SLA with a 12V 10ah at home in reserve. If I had a rickshaw to pull behind me maybe I could!

[RESlusher]

Hey guys! I finally got around to taking some pics of the backpack portable Yeasu FT-8900.

Here's one of the backpack itself. I picked it up off eBay for a steal.



This is one of the finished frame in the pack...



I got a little creative and added a PVC T's on each side of the frame then JB Welded a 3/4" nut inside. I bent some 22 gauge steel bar into scissor legs so I can improved the stability when using the radio outside the pack.



Something else I did was use a piece of leftover 26 gauge steel from the frame cut into a square. I epoxied the mounting bracket for the radio to this square. Holes were drilled in each of the corners and screws and wing nuts added. This was I can take the radio off the frame and either use it on a table top or in my vehicle.

The downside of all this is that using Red-to-Red and Black-to-Black was too tough for me because I cross wired mine going red-to-black and black-to-red. So I blew the reverse polarity diode in the radio and it has to go to the shop for repair.

I'm hoping to have it ready for use long before Summer Field Day.

[Rt169Radio]

Cool, its looks good, and heavy at the same time.

[gewecke]

You might think about a clear waterproof bag for the mic as well, unless being caught in the rain is not a possibility? Otherwise nice job!

73,
n9zas

[RESlusher]

Originally Posted by Rt169Radio

Cool, its looks good, and heavy at the same time.

The heaviest part is the battery at about 5 lbs. I'll put it on the scale when I get the chance and letcha know.

I put it on my back Sunday afternoon and it didn't feel bad; but after a tactical road march it might be a whole different animal.

[RESlusher]

Originally Posted by gewecke

You might think about a clear waterproof bag for the mic as well, unless being caught in the rain is not a possibility? Otherwise nice job!

73,
n9zas

Thanks! It turned out good right up to the point where I blew the reverse polarity protection diode. Cursed like a sailor when I did that!

Rain's ALWAYS a possibility!

All in all though I like it. Just gotta get one of those Diamond CR8900 antennas. I bought a YoYo-Tenna that will cover everything up to 12m which is more than the radio will do.

[RESlusher]

I got around to weighing the pack fully loaded. It came to 24.8 lbs; but that's with everything in it.